FIG. 10 is a flow chart showing a typical conventional method for manufacturing an optical display unit to be incorporated into an optical display device. First, an optical film manufacturer produces a polarizing sheet material roll, which is a roll of a long sheet material (#1). The sheet material is formed by bonding a release film to a long polarizing sheet material having a polarizer. The specific process of manufacturing such a polarizing sheet material roll is known, and therefore, a description thereof is omitted.
The polarizing sheet material roll is then slit so that a strip-shaped polarizing sheet roll is formed with a width according to the shape of a display substrate (#2). The sheet material drawn from the strip-shaped polarizing sheet roll is then cut into pieces of a specific length according to the shape of the display substrate to be bonded (#3). Therefore, the strip-shaped polarizing sheet with the specific width is cut into polarizing sheet pieces, and a release film is bonded to each of the polarizing sheet pieces, so that pieces of sheet material are obtained. The pieces of sheet material with the specific cut length are subjected to an appearance inspection (#4). Examples of the inspection method include a visual defect inspection and an inspection using a known defect inspection apparatus. The finished products are then inspected (#5). The finished product inspection is based on criteria more stringent than those for the appearance inspection. Subsequently, each end face of the pieces of sheet material is worked (#6). The working is performed to prevent the pressure-sensitive adhesive from coming out of the end faces during transportation. The pieces of sheet material are then each subjected to clean packaging in a clean room environment (#7) and subjected to packaging for transportation (transport packaging) (#8). The pieces of sheet material manufactured as described above are transported to a panel processing manufacturer.
The panel processing manufacturer unpacks the pieces of sheet material transported (#11). An appearance inspection is then performed to check whether scratches, stains or other defects are produced during transportation or unpacking (#12). The pieces of sheet material determined to be non-defective in the inspection are then transferred to the next process. In some cases, this appearance inspection may be omitted. Display substrates (such as glass substrate units each with a sealed liquid crystal cell), to which the pieces of sheet material will be bonded, are previously manufactured and cleaned before the bonding process (#13).
The pieces of sheet material are then bonded to the display substrates, so that optical display units are formed (#14). In this process, a polarizing sheet piece is obtained by peeling off the release film from the piece of sheet material with the pressure-sensitive adhesive layer remaining thereon, and the polarizing sheet piece is bonded to one side of the display substrate using the surface of the pressure-sensitive adhesive layer as the bonding surface. Another polarizing sheet piece may also be bonded to the other side of the display substrate in the same manner. When polarizing sheet pieces are bonded to both sides of the display substrate, they may have the same structure or different structures. Subsequently, the optical display unit formed by bonding the polarizing sheet piece(s) to the display substrate is inspected for bonded state and defects (#15). The optical display unit determined to be non-defective in the inspection is transferred to a mounting process so that it is incorporated into an optical display device (#16). On the other hand, the optical display unit determined to be defective is subjected to a reworking process (#17). In the reworking process, the polarizing sheet piece is peeled off from the optical substrate, and a new polarizing sheet piece is bonded to the display substrate (#14).
The manufacturing process described above particularly requires the steps of working the end faces, packaging the piece of sheet material, and unpacking the piece of sheet material, because the optical film manufacturer and the panel processing manufacturer are located at different places. However, such a multi-step process has not only the problem of an increase in manufacturing cost but also the problem that pieces of sheet material are more likely to be scratched or stained during manufacture.
The technique disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2007-140046 (Patent Document 1) provides a method for solving the problems, which includes the steps of cutting a strip-shaped sheet material being drawn from a strip-shaped polarizing sheet roll and bonding a cut piece of the sheet material to a display substrate, wherein the steps are manufactured on a continuous production line. This makes it possible to improve optical display unit productivity in contrast to the conventional process in which pieces of sheet material are individually packaged and delivered.
Patent Document 1 discloses a process including detecting defects in the sheet material drawn from the strip-shaped polarizing sheet roll and cutting the sheet material based on the result of the detection. More specifically, the sheet material drawn from the strip-shaped polarizing sheet roll is cut in a position depending on the position of the detected defect, and a cut piece of the sheet material is removed as a defective product when it contains a defect(s). Such a process makes it possible to improve the yield of the manufactured pieces of sheet material. In such a process, however, if the strip-shaped sheet material drawn from the strip-shaped polarizing sheet roll has many defects, many regions should be cut and removed from the sheet material. Therefore, the process of manufacturing a strip-shaped polarizing sheet roll by slitting a polarizing sheet material roll should preferably be performed in such a manner that the yield can be further improved.
On the other hand, JP-A No. 2008-116437 (Patent Document 2) discloses a process including detecting defects in a sheet material and analyzing the defect information, which is information about the detected defects, to calculate a yield according to criteria for determining whether the products are non-defective or defective.